Magnetic polymer actuators for microfluidics
PhD project Francis Fahrni
Master student: Willem van Engen
The manipulation of fluids on the sub-millimetre scale - microfluidics - finds application in the miniaturisation and integration of e.g. biological analysis and chemical synthesis. In a microfluidic device, fluids need to be transported, mixed, separated and directed in and through a micro-scale system. The efficient mixing of fluids presents a large challenge in microfluidics. Mixing cannot occur by turbulence because of the low Reynolds number that prevails in micro-channels, and molecular diffusion is rather slow in achieving mixing on the scale of a microfluidic channel. A solution for obtaining mixing on efficient time scales has been to passively or actively manipulate the fluids to induce chaotic advection and increase the interfacial area of two fluids progressively, thereby decreasing the length scale over which diffusion has to take place to mix the fluids.
We investigate magnetic polymer micro-actuators that can be incorporated on the walls of microfluidic channels and can be actuated with magnetic fields. A magnetic stimulus that addresses micro-actuators is very robust, because of the low interaction between magnetic fields and (bio)chemical fluids. The use of polymeric materials for producing micro-actuators potentially allows for cost-effective micro-devices with integrated fluidic actuation.
We develop superparamagnetic and ferromagnetic elastomer composites and investigate techniques to structure them on the micro-scale. We perform actuation of micro-structured actuators with external electromagnets or integrated current wires. For ferromagnetic micro-actuators structured with lithographic and sacrificial layer techniques we are able to control the asymmetry in the actuator movement by tuning the initial remanent magnetisation. An asymmetric movement is crucial in order to obtain a net fluid displacement on a small scale, since viscous forces dominate over inertial forces in the fluid. Local vortices as well as translation flows have been obtained using magnetic polymer actuators inside microfluidic devices (Fahrni et al, Lab Chip 2009).
This PhD project is part of the Polymer MEMS project funded by the Dutch Polymer Institute (DPI, see www.polymers.nl)